Closed loops of cutting wire are used in machines for cutting ingots of hard material such as ingots made of silicon or other semiconductors. The wire cuts the ingot by wear or abrasion. To do this, the machine drives the closed loop to rotate. The velocity of the wire in its longitudinal direction is typically comprised between 5 m/s and 15 m/s. The wire is also held taut with a substantial force typically comprised between 10 N and 50 N and, preferably, between 30 N and 40 N.
The advantage of using a closed loop of cutting wire is that the wire always moves in the same direction and that it is not necessary to make provision to periodically change the movement direction of this wire. Known processes for manufacturing such a closed loop of cutting wire comprise:                manufacturing a cutting wire comprising a central core extending continuously between two free ends, this central core having a tensile strength higher than 1400 MPa; and        welding the two free ends together to form the closed loop of cutting wire.        
Up to now, the weld used to form the loop was produced by heating, for example by means of a laser beam or an electric current, the ends of the cutting wire above the melting point of the central core. Next, the two heated ends were butted together. The molten metal of the central core present on each of these ends mixed and formed the weld after having cooled. Such a process is for example described in U.S. Pat. No. 6,311,684 B1.
It has been observed that during use in cutting machines of such closed loops, the loops thus produced have a tendency to break near the weld in the thermally affected zone. To remedy this problem, U.S. Pat. No. 6,311,684 B1 or patent application WO 99/28075 proposes to apply to the weld additional heat treatments at very precise temperatures. These additional heat treatments complicate the manufacture of the closed loop.
Prior art is also disclosed in GB 892 874 A and FR 88 121 E.
The invention aims to remedy this drawback by providing a simpler process for manufacturing a closed loop of cutting wire.
It therefore relates to such a process according to Claim 1.
Conventional welding processes heat the ends of the steel central core above its melting point. This heating modifies the mechanical properties of the central core locally. More precisely, this decreases its tensile strength and its fatigue strength. It is therefore for this reason that the loop generally breaks near the weld and that U.S. Pat. No. 6,311,684 B1 teaches carrying out additional heat treatments in order to restore the initial mechanical properties of the cutting wire even in the zone affected thermally by the welding.